The present invention relates to the manufacture of electronic devices. More particularly, the present invention relates to improved techniques for etching a transition metal-containing layer during the manufacture of electronic devices.
In the manufacture of certain types of electronic devices, e.g., read/write heads for computer disk drives, integrated circuits, flat panel displays, and the like, a transition metal-containing layer may be employed. As the term is used herein, a transition metal-containing layer generally comprises one or more transition metals or one or more of their alloys. Generally speaking, transition metals include, for example, iron, platinum, cobalt, nickel, as well as copper and/or any of the metals in groups IIIA and IIB of the periodic table. One type of transition metal-containing alloy is, for example, permalloy, which is an iron/nickel/cobalt compound typically employed in the manufacture of thin read/write film heads.
The use of a transition metal-containing layer has posed significant challenges to process engineers since traditional techniques of etching an aluminum metal layer typically do not work well for etching the transition metal-containing layer. By way of example, the etching of the aluminum layer is typically accomplished using Cl.sub.2 since Cl.sub.2 offers a fast etch rate. Further, aluminum chloride is relatively volatile and can be readily pumped or exhausted away from the etch chamber as a byproduct. However, chlorides of transition metals such as nickel chloride, platinum chloride, and the like, are relatively nonvolatile and tend to be redeposited back on the surface of the substrate during etching, with detrimental consequences to etch profile and etch uniformity. By way of example, the presence of chlorides of transition metals on the surface of the substrate represents unwanted residues and may cause difficulties in post-etch masking removal and poor device performance (e.g., electrical shorts due to bridging).
To facilitate discussion, FIG. 1 depicts a layer stack 100, representing an exemplary layer stack which includes a transition metal-containing layer. Although only a few layers of layer stack 100 are shown, it should be understood that other additional layers above, below, or between the layers shown may be present. Accordingly, although the layers are shown to be in direct contact with one another for ease of illustration, these layers may be separated by one or more other layers in a given layer stack, and terms such as "above" or "below" as employed herein do not necessarily require a direct contact between the layers.
As shown in FIG. 1, layer stack 100 includes an underlying layer 102 which may represent any layer or structure underlying a transition metal-containing layer. The exact composition and structure of underlying 102 depends on the electronic device to be fabricated and may represent, in one case, the substrate itself (e.g., the silicon wafer or the glass panel). Above underlying layer 102, there is shown a transition metal-containing layer 104.
A transition metal-containing layer 104 may include, as mentioned, one or more transition metals or one or more of their alloys. To facilitate etching, a photoresist layer 106 is typically deposited above transition metal-containing layer 104 to form a mask. Photoresist layer 106 is patterned to form exemplary openings 108 and 110 into which the transition metal etchant can enter to etch a trench or via in transition metal-containing layer 104.
In the prior art, the etching of a transition metal-containing layer may be accomplished using a sputtering process, which employs, for example, argon as the bombardment agent. Sputtering is essentially a physical etching process and can produce satisfactory etch rates through transition metal-containing layer 104 if appropriately controlled. It has been found, however, that the sputtered transition metal tends to get redeposited on the substrate surface, including the surface of photoresist layer 106, causing difficulties in the subsequent photoresist removal step. Further, a purely physical etch process tends to have a low selectivity to photoresist, i.e., it may unduly damage the protective regions in photoresist layer 106. The photoresist damage issue is of particular concern in the fabrication of modem high density electronic devices since these devices are closely packed together and require a relative thin photoresist layer 106 during fabrication. The small geometry and high aspect ratios in these modem, high density devices also reduce sputtering efficiency due to, for example, charging.
Another prior art process for etching transition metal-containing layer 104 involves the use of an Ar/Cl.sub.2 chemistry in a plasma etch chamber, typically a high pressure/low density plasma etch chamber such as a diode-based etch chamber. As the term is used herein, high pressure processing chambers generally refer to processing chambers whose operating pressure is higher than about 100 mTorr. Cl.sub.2 is selected since it provides the ions for the conversion to the metal chlorides. The etch rate is principally controlled by the sputtering efficiency which is typically lower in the high pressure/low density plasma reactors. The chlorine reactive species combine with the sputtered transition metal to form chlorides of transition metals, which tend to be soluble in water. After etching, a rinse in deionized water tends to remove a major portion of the transition metal chlorides.
It has been found, however, that even the Ar/Cl.sub.2 chemistry produces less than satisfactory transition metal etch rates when employed in the high pressure/low density plasma processing chambers. Further, the Ar/Cl.sub.2 chemistry tends to have a low selectivity to photoresist. In the fabrication of modern, high density electronic devices, this low selectivity to photoresist renders the prior art Ar/Cl.sub.2 chemistry unsuitable for use as a transition metal-containing layer etchant in the fabrication of electronic devices. Accordingly, many manufacturers are forced to use a hard mask due to this lower photoresist selectivity issue.
In view of the foregoing, there are desired improved techniques for etching through a transition metal-containing layer. The improved techniques preferably improve the etch rate through the transition metal-containing layer while increasing the selectivity to photoresist in order to allow the transition metal-containing layer to be employed in modem high density electronic devices.